1. Field of the Invention
The present invention relates to lighter-than-air vehicles, and more particularly to buoyant aerial vehicles having a lifting gas contained in an envelope and sealing balloonlets drifting in the lifting gas for moving toward and sealing tears or ruptures that occur in the envelope.
2. Description of the Related Art
Lighter-than-air vehicles, also known as blimps or dirigibles, have evolved as an important mode of cargo transportation in recent past years. Typically, construction includes a main envelope or pressure hull formed of a fabric which is lightweight, extremely strong and impervious to gas diffusion, as for example, laminated plastic or nylon. The envelope is typically filled with a lighter-than-air gas, such as helium or hydrogen, which imparts lift to the dirigible.
One of the problems encountered with dirigibles is how to repair, while in flight, holes or punctures in the envelope, for if not dealt with in a timely and expeditious manner, the lifting gas will escape from within the envelope and the mission and continued flight of the otherwise buoyant vehicle will be thwarted.
Several devices and techniques for sealing openings, such as rips or punctures, in container walls have been proposed. For example, U.S. Pat. No. 4,088,240 to Miguel teaches attaching a layer of carpet-like material to the inner surface of a fuel tank to permit fibers of the carpet-like material to "flow" into, and thereby effectively "seal", the hole or puncture. Similarly, U.S. Pat. No. 4,422,561 to Grosvenor et al. teaches providing a plurality of fronds permanently attached to tank walls so that the fronds cumulatively move toward an opening or puncture to plug the hole. Other mechanisms for plugging or patching holes in tank walls or other similar structures are disclosed by U.S. Pat. No. 2,422,797 to Pfleumer (sealant layer that flows toward and plugs an opening), U.S. Pat. No. 3,666,133 to Benning (photocurable sealant in wall capable of flowing into and sealing wall openings), and U.S. Pat. No. 3,291,333 to House (two layers of sealant which flow into and seal wall openings). Mechanisms for the intentional deflation of airships are disclosed by U.S. Pat. No. 4,033,527 to Parsons and U.S. Pat. No. 4,432,513 to Yost.
Against this background of known technology, the applicant has developed a new method and apparatus for sealing ruptures in a main envelope filled with a lifting gas. A preferred method entails providing a plurality of small envelopes or balloons, hereinafter referred to as "balloonets", inside the main envelope which preferably are filled with a gas that is lighter than the gas inside the envelope. When a rupture in the main envelope occurs, the balloonets float toward the rupture to plug and seal it from further leakage of the lifting gas.